<template>
  <ul class="list">
    <li class="item"
        v-for="item in letters"
        :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
  export default {
    name: "CityAlphabet",
    props: {
      citys: Object
    },
    data () {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    methods: {
      handleLetterClick(e) {
        this.$emit('change', e.target.innerText);
      },
      handleTouchStart () {
        this.touchStatus = true;
      },
      handleTouchMove (e) {
        if (this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer);
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 94;
            const index = Math.floor((touchY - this.startY) / 20);
            if (index >= 0 && index < this.letters.length) {
              this.$emit('change', this.letters[index]);
            }
          }, 16)
        }
      },
      handleTouchEnd () {
        this.touchStatus = false;
      }
    },
    computed: {
      letters () {
        let letters = [];
        for (let i in this.citys) {
          letters.push(i);
        }
        return letters;
      }
    },
    updated () {
      this.startY = this.$refs['A'][0].offsetTop;
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~@/assets/styles/varibles.styl";
  .list
    position absolute
    display flex
    flex-direction column
    justify-content center
    top 1.78rem
    right 0
    bottom 0
    width .4rem
    .item
      text-align center
      line-height .4rem
      color $bgColor
</style>
